Publications - 2003
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NMR solvent relaxation studies of Na+-montmorillonite clay suspensions containing non-ionic polymers
S. Rossi
Production Department, Research Subsidiary of Petróleos de Venezuela, INTEVEP S.A. PDVSA, Los Teques, Edo. Miranda, Venezuela
P. F. Luckham
Department of Chemical Engineering, Imperial College of Science, Technology and Medicine, Prince Consort Road, London SW7 2BY, UK
N. Green
Zeneca Agrochemicals, Jealott's Hill Research Station, Bracknell, Berkshire RG12 6EY, UK
Terence Cosgrove
School of Chemistry, The University of Bristol, Cantock's Close, Bristol BS8 1TS, United Kingdom
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 215 (1-3), 11-24, 2003 (Copyright 2002 Elsevier Science B.V.)
Abstract
Nuclear magnetic resonance (NMR) relaxation studies were carried out for Na+-montmorillonite aqueous suspensions containing non-ionic surfactants and polymers. The mobility of the solvent was determined by the relaxation time, or specific relaxation rate constant with respect to pure solvent. The adsorption of non-ionic surfactants or polymers onto Na+-montmorillonite reduces the mobility of the solvent molecules in contact with the clay surface and hence enhances the specific relaxation rate. The maximum value for the relaxation rate constant at approximately half of the surfactant particle coverage was interpreted to be due to the formation of `hemi-micelles' on the clay surface, where the ethylene oxide chains are in closest proximity with the surface. For the surfactants studied, the relaxation rate constant was found to increase with the length of the ethylene oxide chain. The subsequent decline of this value was explained by a change in configuration of the surfactant `hemi-micelles' to `oblate-shaped' micelles on the surface of Na+-montmorillonite. A steady increase was found for the relaxation rate constant as a function of the adsorbed amount of polymer, followed by a plateau value. This indicated that the `train density' or fraction of bound polymer had reached a maximum value, the remaining amount of polymer was adsorbed in `loops' and `tails' on the clay surface. However, a significantly higher molecular weight polymer showed an altogether different trend, indicating that a significant rearrangement on the surface took place. The bound fraction at the surface was estimated as a function of the adsorbed amount, and increased with decreasing molecular weight of the polymer.
Inclusion Complex Formed between Star-Poly(ethylene glycol) and Cyclodextrins
Edvaldo Sabadini
Instituto de Quimica, Universidade Estadual de Campinas, Caixa Postal 6154, CEP 13084-862 Campinas, Brazil
Terence Cosgrove
School of Chemistry, The University of Bristol, Cantock's Close, Bristol BS8 1TS, United Kingdom
Langmuir, 19 (23), 9680 -9683, 2003 (Copyright 2003 American Chemical Society)
Abstract
Aqueous solutions of α- and γ-cyclodextrins can form spontaneous inclusion complexes with poly(ethylene glycol), PEG, in which the hydrophobic cavities of the cyclic oligosaccharides can be threaded onto the polymer chain. Linear or multiarm PEGs with low molecular weight can be decorated with cyclodextrins, yielding crystalline phases. In this work, we report for the first time the complexation of cyclodextrin with star-poly(ethylene glycol), s-PEG, with high molecular weight, containing 13 and 15 arms. The final result of the complexation is a hydrogel. The kinetics of gelation is strongly affected by the size of the cyclodextrin cavity. The effects of the polymer molecular weight and number of arms on the yield of the complexation and on the gel structure are discussed.
Rheology, Cryogenic Transmission Electron Spectroscopy, and Small-Angle Neutron Scattering of Highly Viscoelastic Wormlike Micellar Solutions
Vania Croce and Terence Cosgrove
School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, U.K
Geoff Maitland and Trevor Hughes
Schlumberger Cambridge Research, High Cross, Madingley Road, Cambridge CB3 0EL, U.K
Göran Karlsson
Department of Physical Chemistry, Uppsala University, Box 579, Uppsala S-75123, Sweden
Langmuir, 19 (20), 8536 -8541, 2003 (Copyright 2003 American Chemical Society)
Abstract
To understand the strong viscoelastic response showed by aqueous solutions of erucylbis(hydroxyethyl)methylammonium chloride (EHAC) in the presence of potassium chloride (KCl), steady-state rheology, small-angle neutron scattering (SANS), and cryogenic transmission electron microscopy (cryo-TEM) experiments were performed. This cationic surfactant has the ability to self-assemble into giant wormlike micelles. The effect of surfactant concentration, added salt, and temperature were investigated. The surfactant solutions have a gellike behavior at room temperature and become Maxwellian as the temperature is increased. It was found that the low-shear viscosity has a strong dependence on salt concentration and temperature. Small-angle scattering indicated the formation of wormlike micelles. The high-Q range was fitted using the Kratky-Porod wormlike chain model, and a cross-sectional radius of gyration (Rg,xs) of 21 Å was obtained. Additionally, cryo-TEM images revealed changes in the structure of the entangled network with the addition of salt.
Molecular Dynamics Study of Wetting of a Pillar Surface
Mathias Lundgren, Neil L. Allan, and Terence Cosgrove
School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, United Kingdom
Neil George
Syngenta, P.O. Box A38, Leeds Road, Huddersfield, West Yorkshire HD2 1FF, United Kingdom
Langmuir, 19 (17), 7127 -7129, 2003 (Copyright 2003 American Chemical Society)
Abstract
We present results of molecular dynamics simulations of water droplets at pillar surfaces comprised of sheets of carbon atoms. We examine variations in the contact angle with the height of the pillars. A crossover is observed between the Wenzel and Cassie-Baxter regimes when the height of the pillar is changed.
Complexation between α-Cyclodextrin and Poly(ethylene oxide) Physically Adsorbed on the Surface of Colloidal Silica
Edvaldo Sabadini
Instituto de Quimica, Universidade Estadual de Campinas, Caixa Postal 6154, CEP 13084-862 Campinas, Brazil
Terence Cosgrove and Wirach Taweepreda
School of Chemistry, The University of Bristol, Cantock's Close, Bristol BS8 1TS, UK
Langmuir, 19 (11), 4812 -4816, 2003 (Copyright 2003 American Chemical Society)
Abstract
Aqueous solutions of α-cyclodextrin (α-CD), a cyclic oligomer formed by six glucose units, complex spontaneously with poly(ethylene oxide), PEO, and several molecules of a-CD thread onto the host polymer chain. A new nanocomposite has been synthesized by the complexation of PEO physically adsorbed on the surface of colloidal silica with α-CD. The PEO monomers adsorbed on the silica surface were displaced by changing the degree of complexation and the MW of the polymer. As the inclusion of α-CD can only start from the extremity of the PEO chain, the fraction and length of the tails can be studied by changing the number of α-CD molecules threaded. Adsorbed PEO of 1000 molecular weight can be completely included in the cavities of α-CD molecules, resulting in a full displacement of the adsorbed polymer. However, for PEO 6k and 20k, the complexation of the chain is partial, that is, some nonincluded EO units remain adsorbed on the silica surface. In these cases, a gel containing silica was formed in the hydrogel network. The effect of silica on the yield of the complexation was also studied. The solid-state complexes formed by [silica-PEO-α-CD] were characterized by FTIR, SEM, and X-ray diffraction.
Polymer complexes with sugars and surfactants: bulk and interfacial systems
Editor(s): Brian H. Robinson
Terence Cosgrove, Robin Wesley, Julie Joseph, Sarah Mears, Laurie Thompson and Steve Armes
School of Chemistry, University of Bristol, Bristol, UK
Self-Assembly (2003), 187-195. Publisher: IOS Press, Amsterdam, Netherlands
Abstract
In this paper we review our work on the interaction of polymers and surfactants in soln. and at interfaces. A common theme is the change in structure found when polymer chains are decorated with surfactants or sugars.
NMR spin relaxation, self-diffusion and viscosity studies of poly(dimethylsiloxane)s blended with silicate nanoparticles
Claire Roberts, Terence Cosgrove, Randall G. Schmidt, Glenn V. Gordon, Andrew J. Goodwin and Axel Kretschmer
School of Chemistry, University of Bristol, Bristol, UK
ACS Symposium Series (2003), 838(Synthesis and Properties of Silicones and Silicone-Modified Materials), 181-193. Publisher: American Chemical Society
Abstract
NMR spin-spin relaxation and self-diffusion measurements were used to investigate the mobility of poly(dimethylsiloxane) (PDMS) polymers when mixed with trimethylsilyl-treated silicate nanoparticles. The silicate can either solvate or reinforce the composite depending on the size of the particle. The smaller nanoparticle solvated all the polymer samples studied. The larger nanoparticle reinforced the two lowest mol. wt. polymers at any concn. When mixed with the higher mol. wt. PDMS, the larger polysilicate caused a dramatic redn. in the mobility of the polymer chains above a crit. concn.; however, an increase in mobility was obsd. below this crit. concn. This apparent increase in the mobility of the polymer chains was also manifested by a decrease in the zero-shear-rate viscosity of the mixt.
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